A counterbalance system and/or a method for counterbalancing a load

ABSTRACT

Disclosed is a counterbalance system for moving a payload and a method for counterbalancing the payload. The system and method comprise a resilient member that is in communication with the payload to be moved and two resilient members that are in communication with either end of the first resilient member. An actuator is in communication with the first and third resilient members and a payload arm, attached to the payload, is in communication with the first and second resilient members. The resilient members may be compressed and relaxed during movement of the actuator and the payload arm so that energy may be transferred between the system and the payload to counterbalance the weight of the payload.

FIELD OF THE INVENTION

The present invention relates to a counterbalancing system, and moreparticularly to a multiple resilient member system for counterbalancinga payload.

BACKGROUND OF THE INVENTION

Many scientific, medical and industrial tasks involve the deployment ofobjects or instruments, which may need to be held aloft and manipulatedin space for extended periods of time, resulting in repetitive stress tothe user. The resulting repetitive stresses are known to be a cause ofwork-related trauma.

For example, work-related musculoskeletal disorders have been identifiedas a widespread problem amongst diagnostic medical sonographers andvascular technologists. In 2006, approximately 46,000 sonographer andvascular technologist job positions existed in the United States. Arepresentative survey reported nearly 90% of sonographers and vasculartechnologists complete ultrasound scans while in some form of pain.Aggravating factors for pain during procedures was reported bysonographers to include sustained and repeated twisting of the neck andbody, sustained arm abduction and application of pressure on theultrasound transducer.

In a further example, poor ergonomics within industrial settings mayalso adversely affect the productivity and the health and safety ofworkers. Heavy tools or parts may require maneuvering in repetitive orawkward motions by workers within industrial settings. Workers may alsobe required to maintain fixed poses for extended periods of time. Toimprove worker ergonomics, devices have been developed to counterbalancetools or parts. These devices counteract the force of gravity tosimulate the tool floating in air and improve worker ergonomics.

In the field of diagnostic medical sonography and vascular technology,for example, previous counterbalancing arms may have used high torquemotors to counterbalance the load weight creating potential harm for apatient. In the event of a malfunction, the motors may potentially drivethe arm into the patient with a minimum force of twice the weight of thearm. In the event of a power failure, a traditional arm may lose itspose and slump under its own weight as the motors can no longercounterbalance the weight. While brakes may have been applied to preventtraditional arms from slumping in a power failure, the traditional armmay become fully locked (i.e., un-adjustable) until power is restored.

Prior attempts, if any, to solve problems associated with prior artdevices and/or methods may have been unsuccessful and/or had one or moredisadvantages associated with them. Prior art devices and/or methodshave been ill-suited to solve the stated problems and/or theshortcomings which have been associated with them.

Various prior art counterbalance systems have attempted to reduce themany aggravating factors reported by workers in the above-noted fields,including United States Patent Application No. 2010/0319164 forCounterbalance Assembly to Bax et al. (discloses a spring counterbalancesystem only for a single rigid arm or link) and Bax, Jeffrey et al., inMed. Phys., vol 35, no. 12, pp 5397-5410, 2008 entitled MechanicallyAssisted 3D Ultrasound Guided Prostate Biopsy System.

In addition, there may be a number of known articulating arms that areconfigured to support a device of varying masses, but most havesignificant drawbacks. Some of these known arms may use a coiled springhaving a fixed uniform spring rate as described in U.S. Pat. No.8,066,251. In these arms, when the mass is varied, the coiled springassembly disadvantageously may not be adjustable and a swap may need tobe made between devices as well changing the internal component of anarticulating arm (i.e., the spring). Many of these arms may also use aspring-cable-pulley system; particularly with arms consisting of aseries of interconnecting links as the type that may be described inU.S. Pat. Nos. 5,435,515, 7,618,016, and 7,837,674. Previously, it mayalso have been known to use torsion springs in joints of the arm togenerate torque forces which counter the torque loads in the joints ofthe arm. Furthermore, the concept of using a combination of springs andweights to counterbalance a payload may have been known as described inpublished U.S. Application No. 2005/0193451. A link assembly for a robotarm or snake arm consisting of two or more link members/segments inseries that can be manipulated to flow axially along its length to guidea segment end to a given location may be known as described in U.S. Pat.No. 7,543,518. Also, a counterbalanced set-up arm to support a robot armcomprised of multiple joint arms, including a linkage andspring-cable-pulley balancing mechanism may also have been known astaught by U.S. Pat. No. 7,837,674.

Accordingly, there is a need for an improved counterbalancing assemblyfor an arm. What is needed is a counterbalance apparatus and/or methodthat overcomes one or more of the limitations associated with the priorart. It may be advantageous to provide an apparatus and/or method whichallow the user to quickly pick up a payload with minimal effort.

It is an object of the present invention to obviate or mitigate one ormore of the aforementioned disadvantages and/or shortcomings associatedwith the prior art, to provide one of the aforementioned needs oradvantages, and/or to achieve one or more of the aforementionedobjectives of the invention.

SUMMARY OF THE INVENTION

According to an aspect of one preferred embodiment of the invention,there is disclosed a counterbalance system for engaging a payload havinga load vector in the direction of gravity is provided. The systemincludes a payload (K1) member, a payload compensation (K2) member, anactuator compensation (K3) member, an actuator and a payload arm. Thepayload (K1) member is in communication with the payload to be engaged.The payload compensation (K2) member and the actuator compensation (K3)member are in communication with either end of the payload (K1) member.The actuator, having a loaded and an unloaded position, is incommunication with the payload (K1) and the actuator compensation (K3)members, the payload (K1) and the actuator compensation (K3) members maybe adapted to transfer an actuator energy during movement of theactuator between the loaded and unloaded positions. The payload arm maybe adapted to support the payload, having a load-bearing and a neutralposition, in communication with the payload (K1) and the payloadcompensation (K2) members, the payload (K1) and the payload compensation(K2) members may be adapted to transfer a support energy during movementof the payload arm between the load-bearing and neutral positions.Movement of the actuator to the loaded position when the payload arm isin the neutral position, transfers the actuator energy and the supportenergy to generate a lift vector at the payload to counterbalance theload vector.

According to an aspect of one preferred embodiment of the invention, thepayload arm may preferably, but need not necessarily, rotate about afirst pivot and the actuator arm rotates about a second pivot.

According to an aspect of one preferred embodiment of the invention, thepayload (K1) member, the payload compensation (K2) member and theactuator compensation (K3) member may preferably, but need notnecessarily, be adapted to exert an expansion force.

According to an aspect of one preferred embodiment of the invention, thepayload (K1) member, the payload compensation (K2) member and theactuator compensation (K3) member may preferably, but need notnecessarily, be compression springs.

According to an aspect of one preferred embodiment of the invention, thesystem may preferably, but need not necessarily, comprise first andsecond cams adapted to transfer the support energy between the payload(K1) member and the payload compensation (K2) member and third andfourth cams to transfer the actuator energy between the payload (K1)member and the actuator compensation (K3) member.

According to an aspect of one preferred embodiment of the invention, thesystem may preferably, but need not necessarily, comprise first andsecond cams adapted to transfer the support energy between the payload(K1) member and the payload compensation (K2) member and third andfourth cams to transfer the actuator energy between the payload (K1)member and the actuator compensation (K3) member.

According to an aspect of one preferred embodiment of the invention, thefirst and second cams may preferably, but need not necessarily, bemounted eccentrically in relation to the first pivot and the third andfourth cams may preferably, but need not necessarily, be mountedeccentrically in relation to the second pivot.

According to an aspect of one preferred embodiment of the invention, thepayload (K1) member, the payload compensation (K2) member and theactuator compensation (K3) member may preferably, but need notnecessarily, be adapted to exert a compression force.

According to an aspect of one preferred embodiment of the invention, thepayload (K1) member, the payload compensation (K2) member and theactuator compensation (K3) member are preferably, but need notnecessarily, extension springs.

According to an aspect of one preferred embodiment of the invention, thepayload (K1) member and the payload compensation (K2) member arepreferably, but need not necessarily, attached eccentrically in relationto one another to facilitate transfer of the support energy and thepayload (K1) member and the actuator compensation (K3) member arepreferably, but need not necessarily, attached eccentrically in relationto one another to facilitate transfer of the actuator energy.

According to an aspect of one preferred embodiment of the invention, thesystem preferably, but need not necessarily, comprises a brake adaptedto maintain the actuator at a position.

According to an aspect of one preferred embodiment of the invention, theposition of the brake preferably, but need not necessarily, correspondsto with the load vector.

According to an aspect of one preferred embodiment of the invention,there is disclosed a method of engaging a payload having a load vectorin the direction of gravity using a counterbalance system. The methodincludes step (a), (b), (c), and (d). In step (a), a payload (K1) memberis positioned in communication with the payload to be engaged. In step(b), a payload compensation (K2) and an actuator compensation (K3)member are positioned in communication with either end of the payload(K1) member. In step (c), an actuator, moveable between a loaded and anunloaded position, is configured for communication with the payload (K1)and the actuator compensation (K3) members to transfer an actuatorenergy during movement of the actuator between the loaded and unloadedpositions. In step (d), a payload arm adapted to support the payload,moveable between a load-bearing and a neutral position, is configuredfor communication with the payload (K1) and the actuator compensation(K2) members to transfer a support energy during movement of the payloadarm between the load-bearing and neutral positions. Movement of theactuator to the loaded position when the payload arm is in the neutralposition, transfers the actuator energy and the support energy togenerate a lift vector at the payload to counterbalance the load vector.

According to an aspect of one preferred embodiment of the invention, instep (d), the payload arm preferably, but need not necessarily, rotatesabout a first pivot and the actuator arm rotates about a second pivot.

According to an aspect of one preferred embodiment of the invention, insteps (a) and (b), the payload (K1) member, the payload compensation(K2) member and the actuator compensation (K3) member are preferably,but need not necessarily, adapted to exert an extension force.

According to an aspect of one preferred embodiment of the invention, insteps (a) and (b), the payload (K1) member, the payload compensation(K2) member and the actuator compensation (K3) member are preferably,but need not necessarily, compression springs.

According to an aspect of one preferred embodiment of the invention, themethod may preferably, but need not necessarily, further include thestep of configuring first and second cams adapted to transfer thesupport energy between the payload (K1) member and the payloadcompensation (K2) member and third and fourth cams to transfer theactuator energy between the payload (K1) member and the actuatorcompensation (K3) member.

According to an aspect of one preferred embodiment of the invention, thestep of configuring the cams may preferably, but need not necessarily,further include the step of mounting the first and second camseccentrically in relation to the first pivot and the third and fourthcams eccentrically in relation to the second pivot.

According to an aspect of one preferred embodiment of the invention, insteps (a) and (b), the payload (K1) member, the payload compensation(K2) member and the actuator compensation (K3) member may preferably,but need not necessarily, be adapted to exert a compression force.

According to an aspect of one preferred embodiment of the invention, insteps (a) and (b), the payload (K1) member, the payload compensation(K2) member and the actuator compensation (K3) member may preferably,but need no necessarily, be extension springs.

According to an aspect of one preferred embodiment of the invention, themethod may preferably, but need not necessarily, also include a step ofattaching the payload (K1) member and the payload compensation (K2)member eccentrically in relation to one another to facilitate transferof the support energy and the payload (K1) member and the actuatorcompensation (K3) member eccentrically in relation to one another tofacilitate transfer of the actuator energy.

According to an aspect of one preferred embodiment of the invention, themethod may preferably, but need not necessarily, also include a step ofmaintaining the actuator at a position using a brake.

According to an aspect of one preferred embodiment of the invention, themethod may preferably, but need not necessarily, also include a step ofconfiguring the position of the brake to correspond to the load vector.

Other advantages, features and characteristics of the present invention,as well as methods of operation and functions of the related elements ofthe apparatus and method, and the combination of steps, parts andeconomies of manufacture, will become more apparent upon considerationof the following detailed description and the appended claims withreference to the accompanying drawings, the latter of which are brieflydescribed hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are believed to be characteristic of theapparatus and method according to the present invention, as to theirstructure, organization, use, and method of operation, together withfurther objectives and advantages thereof, will be better understoodfrom the following drawings in which presently preferred embodiments ofthe invention will now be illustrated by way of example. It is expresslyunderstood, however, that the drawings are for the purpose ofillustration and description only, and are not intended as a definitionof the limits of the invention. In the accompanying drawings:

FIG. 1 is a schematic representation of a counterbalance system in aparallelogram arm configuration with a payload;

FIG. 2 is a schematic representation of a counterbalance system in alever arm configuration with a payload;

FIG. 3 is a schematic representation of a preferred embodiment of thecounterbalance system of FIG. 2;

FIGS. 4A and 4B are schematic representations of the counterbalancesystem of FIG. 3 with the actuating arm at H⁰ and H¹ respectively;

FIG. 5 is a perspective view of the counterbalance system of FIG. 1;

FIGS. 6A, 6B, and 6C are side views of the system of FIG. 5 with thelifting arm horizontal, raised, and lowered, respectively;

FIG. 7 is a side cross-sectional view of the system of FIG. 5;

FIGS. 8A and B are top views of the system of FIG. 5 with the actuatingarm at H⁰ and H¹ respectively;

FIG. 9 is a bottom view of the system of FIG. 5;

FIG. 10 is an enlarged top view of the system of FIG. 6;

FIGS. 11A and B are a front and rear perspective view, respectively, ofthe system of FIGS. 3, 4A and B with the actuating arm at H⁰;

FIGS. 12A and B are a rear and front perspective view, respectively, ofthe system of FIGS. 11A and B with the actuating arm at H¹;

FIG. 13 is a front perspective view of the system of FIGS. 12A and Bwith the lifting arm raised;

FIGS. 14A and B are plan views of the system of FIGS. 11A and B andFIGS. 12A and B respectively; and

FIGS. 15A and B are plan views of the system of FIGS. 11A and B with theactuating arm at H⁰.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The description that follows, and the embodiments described therein, isprovided by way of illustration of an example, or examples, ofparticular embodiments of the principles of the present invention. Theseexamples are provided for the purposes of explanation, and not oflimitation, of those principles and of the invention. In thedescription, like parts are marked throughout the specification and thedrawings with the same respective reference numerals. The drawings arenot necessarily to scale and in some instances proportions may have beenexaggerated in order to more clearly depict certain embodiments andfeatures of the invention.

In this disclosure, a number of terms and abbreviations are used. Thefollowing definitions of such terms and abbreviations are provided.

As used herein, a person skilled in the relevant art may generallyunderstand the term “comprising” to generally mean the presence of thestated features, integers, steps, or components as referred to in theclaims, but that it does not preclude the presence or addition of one ormore other features, integers, steps, components or groups thereof.

In the description and drawings herein, and unless noted otherwise, theterms “vertical”, “lateral” and “horizontal”, are generally referencesto a Cartesian co-ordinate system in which the vertical directiongenerally extends in an “up and down” orientation from bottom to top(y-axis) while the lateral direction generally extends in a “left toright” or “side to side” orientation (x-axis). In addition, thehorizontal direction extends in a “front to back” orientation and canextend in an orientation that may extend out from or into the page(z-axis). Unless indicated otherwise, the force or vector of gravityacts parallel to the y-axis (e.g., the vertical direction) in a generaldownward manner.

As used herein, a person skilled in the relevant art would understandthat a parallelogram is a quadrilateral with two pairs of parallelsides. The opposite or facing sides of a parallelogram are of equallength and the opposite angles of a parallelogram are of equal measure.Parallelograms may include, but are not limited to, rhomboids,rectangles, rhombuses, and squares. Those skilled in the relevant artwould understand that a parallelogram of the present invention may bedisposed in single or compound linkages, wherein it will be understoodthat a compound parallelogram generally may comprise two parallelogramswith a common side.

As used herein, a person skilled in the relevant art would understandthat a “resilient member” may comprise one or more of any of thefollowing elastic, pneumatic, gas spring, constant force spring motor,or other device adapted to store or exert mechanical energy, generateforce and/or that is back-drivable (e.g., force applied to an output canmove an input). In a preferred embodiment, a resilient member maycomprise a spring-like device and in a more preferred embodiment, maycomprise a compression or extension spring. While springs may preferablybe represented in the figures of the present application, personsskilled in the art will understand that any force generating device maybe used in the system described herein.

As used herein, a person skilled in the relevant art will understand a“spring-like device” to refer to any device or structure that actssubstantially like a compression or tension spring in providingresistance to a linear compression, expansion and/or tension along alongitudinal axis or resistance to bending which may produce a force atright angles to a long axis of the spring (e.g., a leaf or torsionspring). An example of a spring-like device is a unit of rubber or otherresilient material or a pneumatic pressurized cylinder any one of whichmay be used in an equivalent manner to a compression or tension springby providing resistance to a linear force along a longitudinal axis.Another example of a spring-like device is a spring, such as acompression spring or a tension spring. Compression springs are anexample of a low cost force generating device that may be utilized toprovide a simplified arrangement within the counterbalance assembly. Acompression spring includes a longitudinal axis along which linearcompressive forces may be imposed as a result of rotational movement ofa mechanical arm. Examples of compression springs include relativelystandard die springs as commonly available in the industry. The exactnumber and size of such resilient members used in the counterbalanceassembly described herein can vary depending upon the counterbalancetorque desired, the size of the robotic arm involved, and the like, aswill be recognized by the skilled person.

As used herein, a person skilled in the relevant art will be understoodthat a force generating device refers to any structure or device whichprovides resistance to forces (e.g. compressive, expansive or tensileforces) applied thereto or imposed thereon (e.g. linear deflectionforces). It will be also understood that a force generating device maygenerate force. For example, it will be understood that any structure ordevice that exhibits resistance to linear compression or tension alongan axis (e.g. a longitudinal axis) thereof may be useful as a forcegenerating device. It will be further understood, therefore, that aforce generating device may include a longitudinal axis along whichlinear forces may be imposed. As will be understood from the descriptionof the present invention provided herein, a force generating device may,in a preferred embodiment, interact with a cam to convert rotationalmovement into linear deflection of the force generating device. Anexample of a force generating device is a spring-like device. The forcegenerating device may be adjustable such that the resistive forceprovided by the force generating device may be increased or decreased toallow for variation in mechanical arms. A force generating device mayinteract with at least one other element or component of the presentinvention (e.g. a cam, etc.) in accordance with embodiments of thepresent invention.

As used herein, a person skilled in the relevant art will understand a“cam” to refer to component that rotates or reciprocates to provide aprescribed or variable motion in an interacting element, which is oftentermed the follower. Skilled readers may understand that the cam itselfneed not move and may be fixed in place as the component rotates aboutthe cam. In the context of the counterbalance system described herein, acam may be any structure or device that is set relative to a pivot of ajoint, to exert a prescribed or variable motion on an interactingportion of a force generating device as a function of the rotation ofthe joint. More specifically, a cam refers to any structure or devicethat can convert rotational movement of a mechanical arm into a linearmovement parallel to a longitudinal axis of a force generating device.Cams are preferably set eccentrically (i.e., not placed centrally or nothaving its axis or other part placed centrally) relative to a centralaxis of a pivot of a joint of a mechanical arm. A cam may be mountedwithin the circumference of a joint. Alternatively, a cam need not bemounted entirely within the circumference of a joint, and may readily beset outside the circumference of a joint where full rotation isunnecessary or where physical collision or interference of mechanicalcomponents is not a concern, for example as may be the case for largeindustrial robotic arms. Notably, full rotation may still beaccomplished when the cam is positioned outside of the circumference ofthe joint. One example of a cam is an eccentric bearing, such as abearing that is eccentric relative to a central joint or base pivot ofan arm and/or one of the pivots of a parallelogram arm. A cam may alsobe approximated by a lever and bearing system, where, for example, thelever extends from a joint that can interact with a force generatingdevice. Cams can be varied shape so as impart a desired lineardeflection of the force generating device.

Any technique for achieving an interaction of a cam to its followerknown in the art may be used to achieve interaction of a forcegenerating device and a cam in the counterbalance assembly describedherein. Each of the examples described in the Figures may be used toachieve an interaction between a force generating device and a cam.Still other forms of coupling using slots, pegs, pins or othertechniques known in the art can be used to achieve the interaction of aforce generating device and a cam. Interaction as used hereincontemplates a force generating device abutting or engaging a cam, and aforce generating device being linked or coupled to a cam.

There is a need in the art for apparatus and methods for exerting aforce (e.g., to counteract the force of gravity) in order to reduce thephysical effort exerted by users in various settings, including, but notlimited to, medical professionals in performing medical examinations(e.g., ultrasound examinations). More particularly, there is a need inthe art for an apparatus that can counterbalance a load for a userwherein the user can quickly and without additional effort pick up apayload with minimal effort.

An aspect of the present invention thereby preferably provides systemsand methods to reduce the physical strain which may be experienced byusers, including, but not limited to, medical practitioners who performultrasound examinations and similar medical procedures. It will beunderstood, however, that the present invention may be used to assistthe performance of various tasks found in other settings, including, butnot limited to, industrial environments.

A preferred embodiment of the counterbalance system described hereinuses at least two resilient members with each resilient memberinteracting with at least one cam that is mounted eccentrically relativeto a pivot of a joint of a mechanical arm. Functionally, the resilientmember/cam relationships can be divided into first and secondcounterbalance assemblies. The purpose of each assembly is to generatetorque. The torque generated by the first and second assemblies togetherallow the counterbalance system to maintain an equilibrium of torqueexerted on a joint throughout the desired rotation of the joint. Thetorque provided by the first assembly is used to counteract the torqueexerted by the mechanical arm and its associated payload at a rotationalposition, typically horizontal, where torque exerted by the arm isgreatest. The torque provided by the second assembly is to counteractthe linear change in force exerted by the first assembly. For example,the linear change in force due to linear displacement of resilientmembers in the first assembly when the arm is above horizontal resultsin the torque exerted by the mechanical arm being greater than thetorque exerted by resilient member/cam pairs in the first assemblycausing the arm to drift back to horizontal. In contrast, the linearchange in force due to linear displacement of resilient members in thefirst assembly when the arm is below horizontal results in the torqueexerted by the mechanical arm being less than the torque exerted byresilient member/cam pairs in the first assembly causing the arm todrift back to horizontal. The torque provided by the second assembly canmaintain equilibrium when the arm is below and above the horizontal.Thus, the torque provided by the second assembly compensates for thefirst assembly to maintain the arm in positions other than thehorizontal. The horizontal is the rest position, neutral position, ordatum.

Counterbalance systems described herein may maintain equilibrium oftorque for an unlimited degree of rotation. Torque equilibrium may bemaintained for arm rotations greater than 1 degree, 45 degrees, 90degrees, 135 degrees, 180 degrees, 225 degrees, 270 degrees, 315degrees, 360 degrees, and even greater, in both positive and negativedirections.

Counterbalance systems described herein may be used for one or more thanone joint in a mechanical arm.

In order that the invention may be more fully understood, it will now bedescribed, by way of example, with reference to the accompanyingdrawings in which FIG. 1 through FIG. 15 illustrate embodiments of thepresent invention.

Referring now to FIG. 1, there is a schematic illustration of acounterbalance system 100 in accordance with an embodiment of thepresent invention. The system 100 includes a counterbalance arm assembly102 (alternately a first counterbalance assembly) linked with a preloadassembly 104 (alternately a second counterbalance assembly). The system100 further comprises a payload (K1) member 110, a payload compensation(K2) member 112 and an actuator compensation (K3) member 114. In someembodiments, the resilient members 110, 112, 114 are extension springsand are connected (e.g., pinned) such that the payload (K1) member 110is employed in both assemblies 102 and 104. Those skilled in the art,however, will understand that the resilient members 110, 112, 114 mayalso be compression springs in alternate embodiments. An actuating arm120 (alternately, an actuator) is in communication with a lifting arm130 (a parallelogram comprising points A, B, F and I; alternately apayload arm), including a load coupler 132, for engaging a payload 10 tobe held and/or moved. In a preferred embodiment, the load coupler 132may move between points B and F.

Referring to FIG. 2, there is a schematic illustration of acounterbalance system 100 in accordance with an alternate embodiment ofthe present invention. The system 100 includes a counterbalance armassembly 102 linked with a preload assembly 104. The system 100 furthercomprises a payload (K1) member 110, a payload compensation (K2) member112 and an actuator compensation (K3) member 114. In some embodiments,the resilient members 110, 112, 114 are extension springs and areconnected (e.g., pinned) such that the payload (K1) member 110 isemployed in both assemblies 102 and 104. Those skilled in the art,however, will understand that the resilient members 110, 112, 114 mayalso be compression springs in alternate embodiments. An actuating arm120 is in communication with a lifting arm 130 (a simple levercomprising points A and F), including a load coupler 132, for engaging apayload 10 to be held and/or moved.

As shown in FIGS. 1 and 2, assembly 102 includes the payload (K1) member110 and the payload compensation (K2) member 112. The payloadcompensation (K2) member 112 is the compensating resilient member andthe payload (K1) member 110 is the primary resilient member or thecarrying member. The payload (K1) member 110 is responsible forsupporting the weight of the payload 10 (or load vector). The payload(K1) member 110 and payload compensation (K2) member 112 work togetherto support the payload 10 by generating a lift vector. The payloadcompensation (K2) member allows the counterbalance force applied to thepayload 10 to approximate a perfect counterbalance throughout the rangeof motion of the system 100.

As shown in FIGS. 1 and 2, the second counterbalance assembly 104includes the payload (K1) member 110 and the actuator compensation (K3)member 114. In the assembly 104, the actuator compensation (K3) member114 is the compensating resilient member and the payload (K1) member 110is the primary resilient member for supporting the weight of thecounterbalanced payload 10. Persons skilled in the art will understandthat the actuator compensation (K3) member 114 does not impart a directforce to counterbalancing the payload 10 when actuator HG is locked andthat the actuator compensation (K3) member 114 could be removed and thepayload 10 would still be counterbalanced.

As shown in FIG. 3, the system 100 comprises resilient members 110, 112,114 adapted to exert an expansion force (e.g., compression springs). Thepayload compensation (K2) member 112 and the actuator compensation (K3)member 114 are preferably fixed at a base (or grounded fixture) and theother end(s) may in communication with eccentric circular cams 210 a and212 b—e.g., by a yoke (not shown)—such that each cam 210 a, 212 b isfree to rotate about a fulcrum or pivot 170, 172 of a joint, and theresilient members 112, 114 are free to compress (or expand) to generateforce. In preferable embodiments, the ends of the payload (K1) member110 are not fixed and are free to engage cams 210 b and 212 a. Thepayload (K1) member 110 may preferably be axially constrained by a fixedguidance component 111 to maintain the alignment of the member 110 withthe cams 210 b, 212 a. As will be seen in FIG. 3, cam 210 b iseccentrically set relative to the pivot 170 of a joint by a distanceequal to e1, and cam 210 a is eccentrically set relative to the pivot170 of the joint by a distance of e2. Similarly, cam 212 a iseccentrically set relative to the pivot 172 of a joint by a distanceequal to e3, and the fourth cam 212 b is eccentrically set relative tothe pivot 172 of the joint by a distance of e4.

As shown in FIG. 3, the payload (K1) member 110 interacts with cams 210b, 212 a, while the payload compensation (K2) member 112 interacts withthe first cam 210 a, and the actuator compensation (K3) member 114interacts with the fourth cam 212 b. Cams 210 ab are pinned to thepayload arm 130 that supports the payload 10 and cams 212 ab are pinnedto the actuator 120. The compressive (or tensile) force exerted by eachresilient member 110, 112, 114 results in a net torque being exertedabout the first and second pivots 170, 172 of the payload arm 130 andactuator 120, respectively. It will be understood by a person skilled inthe relevant art that there are numerous ways to connect or configurethe payload (K1), the payload compensation (K2) and the actuatorcompensation (K3) members 110, 112, 114 in the preferred embodiments ofthe present invention. Referring to FIG. 3, for example, the resilientmembers 110, 112, 114 are abutting or adjacent to the payload arm 130 byassociating each of the resilient members 110, 112, 114 with the one ormore eccentric cams 210 ab, 212 ab. In a preferred embodiment, theresilient members 110, 112, 114 may slide against the surface of thecams 210 ab, 212 ab (and/or the cams 210 ab, 212 ab may roll against theends of the resilient members 110, 112, 114) such that the point ofcontact of the resilient members 110, 112, 114 on the cams 210 ab, 212ab may change as the payload arm 130 and/or the actuator 120 is rotated.In preferred embodiments, the payload (K1) member 110 is adapted foralignment with cams 210 b, 212 a using a guide (e.g., rail, cylinder) tofacilitate sliding of the member 110 along its long axis. FIG. 3 is aschematic illustration depicting the geometric relationship of theresilient members 110, 112, 114 and cams 210 ab, 210 ab. Persons skilledin the art would understand that in this resilient member-camrelationship, the resilient members 110, 112, 114 exert an extensionforce (e.g., compression springs).

FIGS. 3 and 4 schematically illustrate different orientations ofresilient members 110, 112, 114 and cams 210 ab, 212 ab in a system 100designed to fully support the weight of a payload 10 about a hingedconnection which is connected to a ground or stable fixture. As shown inFIG. 3, one end of resilient members 112 and 114 is anchored to theground (or a fixture) while the lifting arm 130 (pinned to the cams 210ab) and/or the actuating arm 120 (pinned to the cams 212 ab) are free torotate about pivots 170, 172 of the joints of a mechanical arm. Inpreferable embodiments, the ends of the payload (K1) member 110 are notfixed and are free to engage cams 210 b and 212 a. Persons skilled inthe art may understand that the ability to establish equilibrium oftorque relative to pivots 170, 172 is not limited to the specificresilient member-cam orientations shown in FIGS. 3 and 4.

As shown in FIG. 3, the relationship between the payload (K1) member 110and the second cam 210 b to the lifting arm 130 is oriented such thatthe line joining the pivot 170 and e1 is not coincident with the linejoining the pivot 170 to the center of gravity of the payload 10, whichincludes the mass of the lifting arm 130. Persons skilled in the art,however, may understand that as the value of θ₁ is constantly changing,if the arm 130 is in a horizontal position, the line joining the pivot170 and e1 will become coincident with the line joining the pivot 170 tothe center of gravity of the payload 10.

In an example of an alternate orientation shown in FIG. 4, therelationship between resilient member 112 and the second cam 210 b tothe lifting arm 130 is orientated such that the line joining the pivot170 and e1 is coincident with the line joining the pivot 170 to thecenter of gravity of the payload 10, which includes the mass of thelifting arm 130. Persons skilled in the art, however, may understandthat as the value of θ₁ is constantly changing, if the arm 130 movesaway from a horizontal position, the line joining the pivot 170 and e1will not be coincident with the line joining the pivot 170 to the centerof gravity of the payload 10. Likewise, the line joining the pivot 172and e3 is coincident with the line joining the pivot 172 to the centerof gravity of the actuating arm 120. Persons skilled in the art,however, may understand that as the value of θ₂ is constantly changing,if the arm 120 moves away from a horizontal position (H⁰), the linejoining the pivot 172 and e3 will not be coincident with the linejoining the pivot 172 to the center of gravity of the actuating arm 120.

In both FIGS. 3 and 4, the orientation of the relationship of theresilient members 110,112,114 to the cams 210 ab,212 ab is preservedthroughout the rotation of the arms 120, 130. Thus, if the cams are in apreferred position with respect to the pivots, that will define theorientation of the resilient member in space. If the resilient member isin a desired position in space, that will define the position of the camwith respect to the pivot. Referring to FIG. 3, there is depicted anexample where the user may place the resilient members or cams in anyorientation in space as long as the resilient member-cam pairs satisfythe equations provided in U.S. Patent Application No. 2010/0319164(incorporated herein by reference).

As shown in the configuration of FIG. 4A, given the orientation of thesecond cam 210 b to the lifting arm 130, the resilient member 110 ispreferably adapted for a vertical position. The payload (K1) member 110preferably approximates a perfect balance of the payload 10 when the arm130 is horizontal (θ₁=0 degrees) and members 110, 112 are exerting atensile force. However, persons skilled in the art may understand thatgiven the configuration of the cams 210 a,b, only the payload (K1)member 110 causes a rotational movement on the arm 130. As the arm 130moves away from the horizontal, the counterbalance force from thepayload (K1) member 110 no longer approximates a perfect counterbalanceand the payload compensation (K2) member 112 is required to correct forthis error. As the arm 130 rotates from horizontal, the payload (K1)member 110 will begin to exert a rotational moment on the arm 130because of the cam 210 b.

The relationship between the payload (K1) member 110 and the payloadcompensation (K2) member 112 and how they counterbalance the payload 10is outlined in U.S. Patent Application No. 2010/0319164 (incorporatedherein by reference). As shown in the in FIGS. 1 to 4, the presentinvention is a novel method to preload the payload (K1) member 110quickly and easily for payloads having different and/or unknown weights.The purpose of the present invention is to avoid the user being requiredto set initial compression offsets.

In FIGS. 4A and B, the relationship between resilient member 112 and thefirst cam 210 a to the lifting arm 130 is orientated such that the linejoining the pivot 170 and e1 181 is coincident with the line joining thepivot 170 to the center of gravity of the payload 10, which includesmass of the lifting arm 130. Persons skilled in the art, however, mayunderstand that as the lifting arm 130 rotates away from horizontal, theline joining the pivot 170 and e1 will not be coincident with the linejoining the pivot 170 to the center of gravity of the payload 10. Inpreferable embodiments, the resilient member 112 may be aligned with thefirst cam 210 a using a guide (e.g., rail, cylinder). In the specificexample shown in FIGS. 4A and B, resilient member 112 is not adjustable,and is set by design such that the resilient member 112 exerts no loadon the first cam 210 a when the lifting arm 130 is in a verticalorientation (90 or 270 degrees relative to a Cartesian coordinate systemwhere 0 degree corresponds to the positive X axis).

Still referring to FIGS. 4A and B, the relationship between eachcam-resilient member pair is such that each cam is 180 degrees out ofphase with each other (i.e., pivot 170 is in-between the eccentricpoints e1 181 and e2 182 and pivot 172 is in-between the eccentricpoints e3 183 and e4 184). In this configuration, each of the resilientmembers is constrained to be 90 degrees out of phase with each other(perpendicular). The relationship created from the constrainedrelationship between each resilient member/cam pair is the torqueexerted by resilient member 112 leads, or lags, resilient member 110 by90 degrees and the torque exerted by resilient member 112 leads, orlags, resilient member 114 by 90 degrees.

In an alternate embodiment, each resilient member/cam pair can berotated about pivots 170, 172 to any position (for example, resilientmembers are aligned, 0 or 180 degrees) as long as the relationshipbetween the cam and corresponding resilient member is maintained.

Thus, the ability to establish equilibrium relative to pivots 170, 172is not limited to specific resilient member-cam orientations shown inFIGS. 3 and 4 as will also be apparent from equilibrium equationsprovided in the following paragraphs.

The following is a description of the equilibrium equations that governthe geometric resilient member/cam relationships shown in FIGS. 3 and 4.The force friction has been omitted from this analysis as it has nobearing on the equilibrium equations when the machine is at rest.Friction can be used as an advantage to construct inexpensive mechanismsthat behave in a similar manner to the case illustrated in FIGS. 3 and 4but do not fully balance the load. The sum of all the frictional forcesbetween every moving part within the mechanism would prevent drift.

Referring to FIG. 3, equilibrium about the pivot 170 is established whenthe net torque is zero, i.e.:

T _(g) +T _(x) +T _(y)=0   (1)

where Tg is the unbalanced torque due to the payload 10, and theunbalanced torque produced from resilient members 110 and 112 are T_(x)and T_(y) respectively. The unbalanced torque produced by the weight isthe product of the gravitational force due to the payload M, and theshortest distance between the force vector (M=mg) and the pivot 170:

T _(g) =Mr cos(θ₁)   (2).

Where “r” is the distance between the pivot 170 and the center of massof the payload 10 and θ₁ is the angle between horizontal (x-axis) andthe line joining the center of gravity of the payload 10 and pivot 170.

The net torque of resilient member 110 about pivot 170 is equal to thesum of the torque produced from the compression of the resilient memberdue to the arm displacement θ₁ 190 and the pre-compression of theresilient member 112 when the arm is horizontal (190: θ₁=0), and isgiven by:

T _(y)=−(K _(y) e ₁ sin(θ₁)+K _(y) Δy)(e ₁ cos(θ₁))   (3),

where K_(y) is the resilient member 110 rate, and Δy is the displacementof the resilient member from rest when the arm is horizontal. The nettorque produced from resilient member 112 is given by:

T _(x) =K _(x) e ₂ ² cos(θ₁)sin(θ₁)   (4),

where K_(x) is the resilient member 112 rate and is uncompressed whenthe arm is in a vertical orientation (up or down). Substitutingequations (2-4) into 1 gives the following:

Mr cos(θ₁)−K _(y) Δye ₁ cos(θ₁)+K _(x) e ₂ ² cos(θ₁)sin(θ₁)−K _(y) e ₁ ²sin(θ₁)cos(θ₁)=0   (5).

Equation 5 is equal to zero and independent of the angle θ₁ under thefollowing conditions:

Mr=K_(y)Δye₁   (6),

K_(x)e₂ ²=K_(y)e₁ ²   (7).

Equation 6 provides that resilient member 110 pre-compression Δy is setto counterbalance the payload 10 at the arm position within the desiredrotation where the torque exerted is greatest, typically when the arm ishorizontal. Equation 7 provides the physical constraints which governthe relationship of each resilient member-cam pair.

Equation 5 can be expanded and written in the following form:

Mr cos(θ₁)−(K _(y) aΔy _(a) e ₁ a+K _(y) bΔy _(b) e _(1b)+ . . .)cos(θ₁)+(K _(xa) e _(2a) ² +K _(xb) e _(2b) ²+ . . . )cos(θ₁)sin(θ₁)−(K_(ya) e _(1a) ² +K _(yb) e _(1b) ²+ . . . )sin(θ₁)cos(θ₁)=0   (8).

Equation 8 is equal to zero and independent of the angle θ₁ under thefollowing conditions:

Mr=K _(y) aΔy _(a) e _(1a) +K _(yb) Δy _(b) e _(1b)+ . . .   (9),

K _(xa) e _(2a) ² +K _(xb) e _(2b) ² + . . . =K _(ya) e _(1a) ² +K _(yb)e _(1b) ²+ . . .   (10).

From equations 9 and 10, the following illustrative embodiments areapparent:

The resilient member 110 and the second cam 210 b can be replaced withmultiple resilient member and cam assemblies.

If (e_(1a) ²=e_(1b) ²= . . . ) and (K_(ya)=K_(yb)= . . . ) then theresilient member 110 can be replaced by multiple resilient membersacting against the second cam 210 b.

The resilient member 112 and the first cam 210 a can be replaced withmultiple resilient member and cam assemblies.

If (e_(2a) ²=e_(2b) ²= . . . ), and (K_(xa)=K_(xb)= . . . ) then theresilient member 112 can be replaced by multiple resilient membersacting against the first cam 210 a.

If multiple resilient members are used in place of 110, then eachresilient member can be preloaded a different amount to offset thepayload when the arm is horizontal.

In FIGS. 3 and 4 when the illustrated mechanism is in balance, thetorque exerted by the payload is equal and opposite to the torqueexerted by the resilient members, regardless of the angular orientationof the arm 130. As illustrated in equation (7), this condition is metwhen the product of e1 squared and Ky is equal to the product of e2squared and Kx. If e1 and e2 are equal, then both resilient members musthave the same spring rate (Kx=Ky).

If tension springs are used in place of compression springs in FIG. 3,then placing the payload on the opposite side of the pivot (or rotatingboth cams 180 degrees), equilibrium about the pivot 170 is establishedwhen the net torque is zero, i.e.:

−T _(g) −T _(x) −T _(y)=0   (1),

where −Tg is the unbalanced torque due to the payload 10, on theopposite side of the pivot 170 illustrated in FIG. 3, and the unbalancedtorque produced from tension resilient member 110 and 112 are −Tx and−Ty respectively. The unbalanced torque produced by the weight is theproduct of the gravitational force due to the payload M, and theshortest distance between the vector (M) and the pivot 170:

−T _(g) =−Mr cos(θ₁)   (2).

The net torque of resilient member 110 about pivot 170 is equal to thesum of the torque produced from the extension of the resilient memberdue to the arm displacement 190 and the pre-tension of the resilientmember when the arm is horizontal (190: θ₁=0), and is given by:

T _(y)=+(K _(y) e ₁ sin(θ₁)+K _(y) Δy)(e ₁ cos(θ₁))   (3),

where Ky is the resilient member rate of 110, and Δy is the displacementof the resilient member from rest when the arm is horizontal. The nettorque produced from resilient member 112 is given by:

T _(x) =−K _(x) e ₂ ² cos(θ₁)sin(θ₁)   (4),

where Kx is the resilient member rate of 112 and is uncompressed whenthe arm is in a vertical orientation (up or down). Substitutingequations (2-4) into 1 gives the following:

−Mr cos(θ₁)+K _(y) Δye ₁ cos(θ)−K _(x) e ₂ ² cos(θ₁)sin(θ₁)+K _(y) e ₁ ²sin(θ₁)cos(θ₁)=0   (5).

Since this is equation 5, then it becomes apparent that tension-typeresilient members can be used as a replacement for compression-typeresilient members.

While the figures show counterbalance systems for a joint of amechanical arm where the assembly comprises three resilient members, theskilled person having the benefit of reviewing the figures willrecognize that the counterbalance assemblies need not be restricted toresilient member balance mechanisms and will further recognizeequivalent counterbalance assemblies.

Other examples by which the resilient members can be connected are knownto those skilled in the art. Specifically, instead of using theresilient member-to-cam interaction, the resilient members 110, 112, 114may be connected using a pinned connection (as best shown in FIG. 5) ateach end to the arm such that the pinned connection is offset from anarm pivot. This type of connection creates an eccentric relationshipequivalent to the resilient member-to-cam embodiment described above(and shown in FIG. 3), as illustrated in FIG. 3 of U.S. PatentApplication No. 2010/0319164 incorporated herein by reference, whichdoubles the stroke of the resilient member by allowing both tension andcompressive loads while only compressing the resilient member in eachcase.

Referring to FIGS. 1, 2 and 3, the arm may be pivotally connected to thesystem via a pivot point or via a parallelogram linkage. Other means bywhich the arm can be connected to the system are known in to personsskilled in the art and include, for example, a spherical linkage (e.g.,see FIG. 2 of Med. Phys., vol 35, no. 12, pp 5397-5410, 2008,incorporated herein by reference).

A user can adjust the carrying capacity of the lifting arm 130 withminimal effort. Persons skilled in the art would understand that if thefirst and second counterbalance assemblies 102,104 are modeled using themechanism described in FIG. 1a of U.S. Patent Application No.2010/0319164, then minimal effort would be required by the user to movethe payload 10.

In operation, referring to FIGS. 1 to 4, a user can operate thecounterbalance system 100 using the following steps:

The payload (K1) member 110 is uncompressed when the payload 10 is notsupported by the lifting arm 130 (A-M) (FIG. 4A is a resting or neutralposition before the load 10 is moved, whereby the payload compensation(K2) member 112 and the actuator compensation (K3) member 114 arecharged and the actuator 120 is preferably adapted to transfer potentialenergy to the payload 10);

The payload compensation (K2) member 112 is uncompressed when θ₁ 190 isequal to +/−90 degrees;

The actuator compensation (K3) member 114 is uncompressed when θ₂ 192 isequal to +/−90 degrees;

K1*(e ₁ ²)=K2*(e ₂ ²); and

K1*(e ₃ ²)=K3*(e ₄ ²).

Referring to FIG. 4A, there is illustrated a counterbalance system 100with a payload 10 having unknown mass coupled to lifting arm 130(alternatively referred to as beam AM 130). In this example, gravity (G)is pointing down, at a right angle to beam AM 130. Persons skilled inthe art will understand that beam AM 130 does not have to be horizontalto pick up and/or support a payload 10. As shown in FIG. 4A, theactuator compensation (K3) member 114 is pre-compressed such that itbecomes relaxed when the actuating arm 120 (alternatively referred to ashandle A′H 120) is rotated plus/minus 90 degrees. As shown in FIG. 4A,the payload compensation (K2) member 112 is pre-compressed such that itbecomes relaxed when the beam AM 130 is rotated so that the beam AM 130is aligned with the force of gravity (G). As shown in FIG. 4A, thepayload (K1) member 110 is uncompressed at the same time the actuatorcompensation (K3) member 114 is compressed to its maximum extent.

To pick up a payload 10, the user rotates the handle A′H 120counterclockwise from H⁰ to H¹. If K1*(e₃ ²)=K3*(e₄ ²), the user willfeel little to no perceivable resistance because the potential energyfrom the actuator compensation (K3) member 114 is redirected to thepayload (K1) member 110 as a preload, which is equal to K1*e₃*sin(θ₂).

At the point when the payload (K1) member 110 is completely supportingthe payload 10, the user will feel an increasing resistance when tryingto rotate the handle A′H 120 beyond point H¹.

Referring to FIG. 4B, if the handle A′H 120 is secured in position H¹,the payload 10 will be fully supported by the payload (K1) member 110and the payload compensation (K2) member 112 if K1*(e₁ ²)=K2*(e₂ ²). Insome preferred embodiments, the beam A′H 120 may be secured using abrake (as best shown in FIGS. 11 to 13) that will not release unless thearm A′H 120 is in a safe position, as best illustrated in FIG. 3 aslever XYZ. The braking mechanism is a self-locking brake. The brake ispreferably required for the system 100 to operate. If the rotation ofA′H 120 is not restricted by the brake, arm A′H 120 will rotate andcause the counterbalance force to be lost (i.e., the energy stored inthe payload (K1) member 110—for example, support energy—will betransferred back into the actuator compensation (K3) member 114).

Still referring to FIG. 3, if the angle XYH is less than the criticalvalue, which is typically about 7 degrees and depends on the brake andthe drum material, no actuation force needs to be applied for braking.Also, the brake will not slip and cannot be released by the user ifthere is a difference in the current energy level of the payload 10 andthe point where the payload 10 is picked up. This will prevent the userfrom releasing the payload 10 when it is unsafe to do so. The range ofmotion is 360 degrees provided that the payload (K1) member 110 and thepayload compensation (K2) member 112 have enough stroke to allow forthis motion. If the counterbalance system 100 is more compact, then thestroke will be shortened thereby limiting the range of motion. As longas the payload (K1) member 110 and payload compensation (K2) member 112are not over-compressed, a full 360 degrees range of motion is possible.

As can be seen in FIGS. 3 and 4, the relationship between the cams 210ab, 212 ab and eccentrics e1,e2,e3,e4 is preferably the same for thefirst counterbalance assembly 102 and the second counterbalance assembly104. In operation, rotation of the actuating arm 120 will cause theforce exerted by the payload (K1) member 110 and the actuatorcompensation (K3) member 114 to change, while the force exerted by thepayload compensation (K2) member 112 remains unchanged. Rotation of thelifting arm 130 will cause the force exerted by the payload (K1) member110 and the payload compensation (K2) member 112 to change, while theforce exerted by the actuator compensation (K3) member 114 remainsunchanged. As the first cam 210 a is 90 degrees out of phase with thesecond cam 210 b, and the third cam 212 a is 90 degrees out of phasewith the fourth cam 212 b, movement of the load 10 (having a loadvector) attached to the lifting arm 130 transfers energy between thepayload (K1) member 110 and the actuator compensation (K3) member 114and movement of the actuating arm 120 transfers energy between thepayload (K1) arm 110 and the payload compensation (K2) arm 112. Thedirection of energy flow preferably depends on the direction of rotationof the actuating arm 120 and the lifting arm 130. For example, if theload 10 is lifted, then both the payload (K1) member 110 and the payloadcompensation (K2) member 112 will lose energy (for example, supportenergy) to the payload 10. In some embodiments, the transfer of energy(for example, actuator energy) between the actuator compensation (K3)member and the payload (K1) member may be prevented by engagement of abrake 122 (as best seen in FIGS. 11 to 13). As the system 100 ispreferably a closed system, the sum of the potential energy of themembers 110, 112, 114 and the load 10 is a constant (i.e.,PE_((K1)member)+PE_((K2)member)+PE_((K3)member)+PE_(load)=constant).

FIG. 5 shows an alternate embodiment of the system 100 of the presentinvention in which the resilient members 110,112,114 are extensionsprings. As before, the system 100 may be divided into a counterbalancearm assembly 102 and a preload assembly 104. The system 100 shownconsists of a forward base plate 140, a rear base plate 150, and fourstabilizing members 160 abcd which form a parallelogram linkage. Thelifting arm 130, accordingly, consists of a single parallelogram segmentand preferably contains two resilient members 110,112. As in theprevious design, the payload (K1) member 110 may be adjustable tosupport payloads 10 of different weights and the payload compensation(K2) member 112 preferably corrects errors in the payload (K1) member110 as the arm 130 moves through its full range of motion. The tworesilient members 110,112 are preferably mounted eccentrically with a 90degree shift.

FIGS. 6A, 6B, and 6C demonstrate the range of motion of the lifting arm130. As shown in FIG. 6A, when the system 100 is in a neutral state(i.e., neither lifting nor lowering a payload 10), the payload (K1)member 110 is preloaded and the payload compensation (K2) member 112 isat a maximum extension. Persons skilled in the art, however, willunderstand that due to the eccentricity, the payload compensation (K2)member 112 is exerting zero moment on the arm 130. As shown in FIG. 6B,when the system 100 is used to lift a payload 10 (not shown) into aload-bearing position, the payload (K1) member 110 is compressed and thepayload compensation (K2) member 112 is compressed. As shown in FIG. 6C,when the system 100 is used to lower a payload 10 (not shown) in theload-bearing position, the payload (K1) member 110 is extended and thepayload compensation (K2) member 112 is compressed.

FIG. 7 shows a side view of the arm 130 in cross-section to better viewthe relationship of the payload (K1) member 110 to the payloadcompensation (K2) member 112.

In the present embodiment, the method of preloading the payload (K1)member 110 is novel. In the prior art, the resilient member 110 may havebeen preloaded using a wrench to turn a preload nut. In the system 100of the present invention, the payload (K1) member 110 is preloaded usinga preload assembly 104 (also known as the second counterbalanceassembly). One end of the payload (K1) member 110 is attached to theforward base plate 140 and one end is attached to the preload assembly104. Previously, the adjustable payload (K1) member 110 was attachedbetween two base links (not shown). The payload (K1) member 110 isattached eccentrically to the actuator 120 of the preload assembly 104.The payload (K1) member 110 has zero preload when the preload assembly104 is at its home position (H⁰) (also referred to as the unloadedposition; not shown) and maximum preload when the preload assembly 104has rotated 180 degrees (H¹) (also referred to as the loaded position;not shown). Rotating the preload assembly 104 counterclockwise will drawthe payload (K1) member 110 back to preload it and increase the payloadcapacity of the arm 130.

FIGS. 8A and 8B show the preload assembly 104 rotating 90 degrees fromits unloaded position (H⁰) to preload the payload (K1) member 110. Thepreload distance of the payload (K1) member 110 is dependent on theeccentric sizing of the resilient member attachment point 124 on theactuator 120. If the preload assembly 104 is rotated 90 degrees thepreload distance is equal to the eccentric size. If the preload assembly104 is rotated 180 degrees the preload distance is approximately equalto twice the eccentric size. The preload assembly 104 prevents theactuator 120 from rotating clockwise in order to maintain the preloadand prevent the payload (K1) member 110 from unloading.

As the preload assembly 104 is rotated, the user may experienceincreasing resistance from the payload (K1) member 110 as it extends. Ifthe member 110 is extremely stiff, the user will be required to exert asignificant amount of force and may experience difficultly in rotatingthe actuator 120. The addition of the actuator compensation (K3) member114 allows the user to rotate the actuator 120 with a minimal level ofexertion. The actuator compensation (K3) member 114 is preferablymounted perpendicularly to the first and second resilient members110,112. The actuator compensation (K3) member 114 is attached to theactuator 120 eccentrically. The eccentric for the actuator compensation(K3) member 114 is shifted 90 degrees from the eccentric for the payload(K1) member 110. The actuator compensation (K3) member 114 acts tocounterbalance the force of the payload (K1) member 110 on the actuator120 and considerably reduces the force the user must exert to preloadthe payload (K1) member 110.

The principals and equations governing the relationship between thepayload (K1) member 110 and the actuator compensation (K3) member 114are preferably, but need not necessarily, exactly the same as therelationship between the payload (K1) member 110 and the payloadcompensation (K2) member 112. To achieve counterbalancing of the payload10 and minimal user exertion during payload (K1) member 110 preloadingthe following relationship must be true:

K _(K1)*(e _(K1))² =K _(K2)*(e _(K2))²   (1);

and

K _(K1)*(e _(K1))² =K _(K3)*(e _(K3))²   (2),

where “K” is the respective resilient member constants of the differentmembers 110,112,114 and “e” is the respective resilient membereccentricities of the different members 110,112,114. The resilientmember eccentricities of the arm are identified in FIGS. 1 to 4.

FIG. 9 depicts a bottom plan view of the system 100. The resilientmembers 110, 112, 114 are shown, notably including the actuatorattachment point 126, which may define an eccentricity, for the actuatorcompensation (K3) member 114.

As seen in FIG. 10, there is an enlarged cross-sectional view of theactuator 120, a handle member 116 and the actuator compensation (K3)member 114. Member 116 is preferably used to automatically lock thebrake 122 to prevent the actuator 120 from moving away from position H¹.

Referring to FIG. 11A, there is depicted a preferred embodiment of thesystem 100 as described schematically in FIGS. 3 to 4, in which theresilient members 110,112,114 are compression springs. As previously,the system 100 may be divided into a counterbalance arm assembly 102 (orfirst counterbalance assembly) and a preload assembly 104 (or secondcounterbalance assembly). The system 100 shown consists of a forwardbase plate 140 and a rear base plate 150. The lifting arm 130 (orpayload arm) is in communication with the payload (K1) and payloadcompensation (K2) members 110, 112. The payload (K1) and payloadcompensation (K2) members 110, 112 are mounted on first and second posts310 (as seen in FIG. 11B), 312 respectively. Cams 210 ab abut member 112and 110 respectively. The payload (K1) member 110 may be adjustable tosupport payloads 10 of different weights and the payload compensation(K2) member 112 preferably corrects errors in the member 110 as the arm130 moves through its full range of motion about pivot 170.

Also seen in FIG. 11A is the second counterbalance assembly 104, whichextends from the rear base plate 150 and includes the third resilientmember 114 mounted on a third post 314. Cam 212 b abuts member 114. Thesecond counterbalance assembly 104 may preferably, but need notnecessarily, be moved about pivot 172 using the actuating arm 120 (oractuator), which may also be used to engage and/or disengage the brake122.

The second counterbalance assembly 104 of this preferred embodiment isbest depicted in FIG. 11B. The second assembly 104 comprises theactuator compensation (K3) member 114 supported by the third post 314and adapted to interact with the fourth cam 212 b which is mountedeccentrically relative to the second pivot 172. The second assembly 104may be rotated about the second pivot 172 using the actuating arm 120(which is in the non-payload engaging, unloaded, or H⁰ position) andreversibly locked in position by the brake 122. As previously mentioned,the second assembly 104 also comprises the payload (K1) member 110 (notshown), supported by the second post 312 (not shown), which is incommunication with the third cam 212 a mounted eccentrically relative tothe second pivot 172.

FIGS. 12A and B depict the system 100 (as shown in FIGS. 11A and B) froma rear and front perspective respectively, whereby the secondcounterbalance assembly 104 has been rotated about the second pivot 172to a payload engaging, or loaded, position (H¹). The actuatorcompensation (K3) member 114 expands as the cam 212 b rotates aboutpivot 172. Payload (K1) member 112 compresses as cam 212 a rotates aboutpivot 172 and the second post 312 is pressed against cam 210 b.

FIG. 13 depicts the system 100 (as shown in FIGS. 11A and B) from afront perspective with the lifting arm 130 rotated vertically about thefirst pivot 170. The payload (K1) member 110 expands as the lifting arm130 is raised and the cam 210 b rotates about pivot 170.

FIGS. 14A and B show a top view of the system 100 (as shown in FIGS. 11Aand B) with the second assembly 104 in a non-payload, unloaded, engaging(i.e.,) H⁰ and payload, or loaded, engaging (i.e., H¹) positionrespectively. The second assembly 104 is rotated about the second pivot172. The actuator compensation (K3) member 114 expands as the cam 212 brotates about pivot 172 due to rotation of the handle 120 between H⁰ andH¹. Payload (K1) member 112 compresses as cam 212 a (not shown) rotatesabout pivot 172 and the second post 312 is pressed against cam 210 b.

FIGS. 15A and B depict a top view of the system 100, with the secondassembly 104 in a non-payload engaging (i.e.,H⁰ and the lifting arm 130extending out from the page and in to the page, respectively. Actuator120 is in the H⁰, or unloaded, position and the payload arm 130 ispositioned along the z-axis (i.e., out from and into the page,respectively) to demonstrate the compression of the payload (K1) member110 due to rotation of the cam 210 b about the pivot 170.

With reference to FIGS. 8B and 12B, to preload the payload (K1) member110 the user preferably rotates the actuator 120 counterclockwise. Theuser will preferably be required to exert a minimal level of force untilthe payload (K1) member 110 is sufficiently preloaded to counterbalancethe payload 10 coupled to the lifting arm 130. The user may experience asudden increase in resistance turning the actuator 120 when sufficientpreload has been achieved. The user can release the actuator 120 and thebrake (as best shown in FIG. 11B) will lock the actuator 120 in place,preventing the payload (K1) member 110 from pulling the actuator 120 torelease all energy stored in the actuator compensation (K3) member 114.

As shown in FIGS. 11A to 15B, the first cam 210 a is 90 degrees out ofphase with the second cam 210 b (i.e., the first pivot 170 is in betweenthe corresponding eccentric points schematically shown in FIGS. 3 and 4)and the third cam 212 a is 90 degrees out of phase with the fourth cam212 b (i.e., the second pivot 172 is in between the correspondingeccentric points schematically shown in FIGS. 3 and 4). Accordingly,when the actuator 120 is in the non-load engaging position H⁰ (and thepayload arm 130 is in a horizontal position), the first (K2) resilientmember 110 is compressed, the second (K1) resilient member 112 isrelaxed, and third (K3) resilient member 114 is compressed. When theactuator 120 is in the load engaging position H¹ (and the payload arm130 is in a vertical position), the first (K2) resilient member 110 isrelaxed, the second (K1) resilient member 112 is compressed, and thethird (K3) resilient member 114 is relaxed.

FIG. 11B depicts the tripping mechanism or brake 122. The brake 122 ispreferably, but need not necessarily, a friction-based toggle design orany other braking mechanism known to persons of ordinary skill in theart. The brake 122 is normally locked to maintain the preload of thepayload (K1) member 110. However, the user can manually release thebrake 122 to rotate the actuator 120 clockwise and reduce the payload(K1) member 110 preload. The brake mechanism 122 does not need to belimited to this particular architecture. Any of a number of brakedesigns could be used for the system 100 (e.g., a tripping mechanism orsimple lock, as described in greater detail below). In some embodiments,the brake 122 can be adjusted in small increments to allow fine controlof the payload (K1) member 110 preload. In other embodiments, however,the brake 122 may be adjustable in one or more single increments toallow the user, for example, to manipulate a high volume of the samepayload having a known weight. The friction brake design shown isadvantageous over a more common gear and pawl based design since it isnot limited to discrete steps.

In some embodiments, the brake 122, as shown in FIGS. 11A,B, 12A,B and13, may be based on a tripping mechanism. A tripping mechanism maypreferably detect an imbalance, which may be a force-based ordisplacement-based (e.g., a pin from the payload arm 130 adapted toengage with another mechanism to lock a position—such as a ratchetingmechanism). In preferred embodiments, the tripping mechanism comprises afirst and second handle (alternately referred to as the lifting arm 130and the actuator 120 respectively). A user may move the first handlebi-directionally to either pick up or drop off a payload. The secondhandle is adapted to lag behind the first handle such that once atripping condition is met, the second handle may jump forward andmaintain the position of the first handle. In preferred embodiments, thefirst and second handles are connected on opposite sides of the system100. In this way, the brake 122 may be more sensitive because as soon asthe payload 10 begins to pick up, the tripping mechanism engages.Preferably, the user cannot overcome the brake 122 because once thepayload 10 is lifted, the mechanism locks and cannot be overcome by theuser. Persons skilled in the art will understand that many differenttripping mechanisms known in the art may be used in the system 100. Thetripping mechanism may be advantageous in systems 100 adapted to liftpayloads 10 having unknown weights (or load vectors).

In other embodiments, the brake 122, as shown in FIGS. 11A,B, 12A,B and13, may be based on a fixed position of the handle 120 (i.e., if theweight of the payload 10, or its load vector, is known). The system 100may comprise a fixed brake 122 that will automatically stop the actuator120 at a set, or predetermined, position (i.e., “on” or “off”). Forexample, if a payload of 50 lbs is picked up, a user can move theactuator 120 to a position corresponding to 50 lbs and then move thepayload arm 130 to pick up the payload 10. This may be accomplished, forexample, by a hook. This simple lock configuration, may be advantageousin situations where a user will be picking up the same payload 10repeatedly as the complexity of the system 100 may be reduced byremoving the tripping mechanism. Skilled readers will understand thatsystems 100 not having a tripping mechanism will still allow for thecounterbalancing of payloads 10; however, the user will require apre-determined position for the actuator 120 and configure the system100 to maintain the actuator 120 in the pre-determined position.

In summary, the counterbalance system 100 contains two counterbalanceassemblies 102,104. Each counterbalance contains two resilient members(i.e., 110 and 112 for the counterbalance arm assembly 102; 112 and 114for the preload assembly 104). The payload (K1) member 110 is common toboth assemblies 102,104 resulting in a total of three resilient members110, 112, 114. The counterbalance arm assembly 102 counterbalancespayloads 10 coupled to the lifting arm 130 by generating a lift vector.The preload assembly 104 is used to preload the payload (K1) member 110of the counterbalance system 100. The actuator compensation (K3) member114 is used to counterbalance the force experienced by the user as theyrotate the preload assembly 104 to preload the payload (K1) member 110.

In a preferred embodiment, the system of the present invention may beapplied in the design of a fully automated robotic arm for medicalapplications in which motors can be mounted onto the device to adjustthe arm pose. Traditional designs may use high torque motors tocounterbalance the arm and payload weight creating potential harm forthe patient. In the event of a malfunction, these motors may potentiallydrive the arm into the patient with a minimum force of twice the weightof the arm. In the event of a power failure, a traditional arm may loseits pose and slump under its own weight as the motors can no longercounterbalance the weight. Brakes can be applied to prevent atraditional arm from slumping in a power failure. However, thetraditional arm will become fully locked and its pose un-adjustableuntil power restored. In comparison, the system of the present inventionis passively counterbalanced using resilient members. As a result,motors having low torque may be used to drive the system and motors arepreferably not required to maintain a given pose. Furthermore, thesystem may be fully back-drivable allowing a given pose to be manuallyadjusted in the event of a power failure. The present system is uniqueamongst medical robotics since the arm provides an additional intrinsiclevel of safety over traditional medical robotic designs.

The system of the present invention preferably allows a user to quicklypick up a payload, having a known or unknown weight, with little or noeffort. The system may be used with many different types of mechanicalarms, including, for example, arms having industrial or medical uses.

Counterbalance systems, for example resilient member balance assemblies,described herein may be used in conjunction with further components asdesired to aid in the orientation of mechanical arms, for example,without limitation, brakes for locking a hinged arm, encoders formeasuring rotational angles of a hinged coupling, counterweights and/orother balances to offset the mass of the system, computer controlledactuators for automating actuation of a hinged coupling. Furthercomponents that may be incorporated into the mechanical arm will beapparent to the skilled person, and suitable combinations of optionalcomponents will also be apparent depending on the particular mechanicalarm and the particular use of the mechanical arm.

As one example of an optional component, a counterweight may be mountedto the arm to offset the mass of a payload and/or mass of one or moreelements of an articulated arm. Although the counterbalance mechanismdescribed herein can eliminate the need for counterweights,counterweights may, if desired, be used in conjunction to offset themass of the system.

As yet another example of an optional component, a braking mechanism maybe mounted within the mechanical arm to inhibit or stop motion of armelements relative to each other.

As still another example of an optional component, the mechanical armmay be equipped with motors (not shown), for example servo motors thatmay be controlled by a computer to automate the motion of variouslinkage elements. The counterbalance mechanism described herein reducesthe force required by motors to actuate the mechanical arm.

As another example of an optional component, in embodiments wheresprings are used in a counterbalance assembly the compression or tensionof one or more springs is adjustable.

Still further optional features will be apparent to the skilled person.

The present counterbalance system may be used in conjunction with manydifferent types of mechanical arms, for example, arms having industrialor medical uses.

The system is preferably, but need not necessarily, capable of handlingpayloads weighing a few grams to about 100 kg and may depend on thelength of the arms 120,130 and their respective ranges of motion.

Referring to FIGS. 4A and B, the counterbalance system 100 ispreferably, but need not necessarily, symmetrical to allow the actuator120 to lift a payload 10, while using the payload arm 130 to adjust forthe payload weight.

The system is capable of handling multiple parts, and can serially pickup and drop off payloads, provided the process can be modeled as aclosed system. Persons skilled in the art will understand that a closedsystem refers to no net gain or loss in the amount of energy storedwithin the three resilient members. While energy may be transferredbetween the resilient members, the total amount of energy between themremains constant. There must be no net energy gain or loss in handlingthe payload from pickup to drop off otherwise the arm must be equippedwith an additional motor or resilient member to absorb the excess energyin the process. For example, an infinite conveyor of 100 lb weightscoming in at one level (“L1”) and the user is lifting a payload to asecond elevational level (“L2”), there is a net energy input that youhave to put in to go from L1 to L2. Once the payload is dropped off, youcannot pick up another payload at the same level, L2 without firstpicking up something of equal weight to that which was dropped off andbringing the arm down to L1. Another resilient member may be added tothis three-resilient member counterbalance system for more energycapture to allow the mechanical arm to pick up and drop off payload inseries. Energy is prestored in the resilient members allowing for oneoperation of the arm from L1 to L2. The motor operates via a feedbackmechanism. It back-drives the energy back to the energy you want it tobe at. At the point at which you drop off the payload, as soon as yousqueeze the lever to release the load.

The present system allows the user to pick up and drop a payload at thesame height. Dropping the load at a different height than picked upwould result in the payload dropping or rising to the same height theload was originally picked up at. This is because there is either anexcess or deficiency in the energy level of the resilient member loadedsystem as the resilient members were preloaded to match the energy levelof the payload at pickup.

If it is desirable to release the payload at a different height than thepickup point, then it is necessary to change the energy level in theK1-K3, or second, assembly to match the height the payload is going tobe dropped off at. To do this a motor (or resilient member and handlecombo like the system used to preload the resilient member K1) is neededto rotate the cam assembly (A′, e3, and e4 in FIG. 3) and the actuatorcompensation (K3) member, but payload (K1) member. Rotating thisassembly clockwise will lower the safe drop off point of the load and acounterclockwise rotation will raise the drop off point of the payload.

If a resilient member-lever mechanism is used in place of a motor, oncethe user releases the load at an elevated height, for example, anotherload would have to be picked up at the drop off height and loweredbefore it is possible to raise a second payload. This limitation onlyapplies to the resilient member-handle option and not the motor as theresilient member can only store a limited amount of energy and the motorhas access to (in theory) an infinite amount of energy from the powergrid.

The commercial applications of the apparatus are preferably wide rangingand span both the medical and non-medical fields. The apparatus may bevaluable for any application where a user may encounter difficultiessupporting or positioning a load (e.g., tool) or is required to quicklypick up a payload. Difficulties with respect to supporting orpositioning the load may arise from: awkward motions, high load weight,maintaining a fixed position for long periods of time, are operatingwithin confined spaces, or high positioning accuracy requirements. Theapparatus of the present invention may be adapted to produce a liftvector to counterbalance the weight of any load (e.g., tool) engaged tothe end of the lifting arm. In some embodiments, payloads, such astools, on the end of the lifting arm can be translated and rotated aswell as remain in position and/or orientation, if desired.

As an example, the system can be used to reduce many of the aggravatingfactors reported by individuals such as sonographers and vasculartechnologists. Loads, such as an ultrasound transducer, can be coupledonto the load bearing arm. The sonographer in this case, could manuallyadjust the position of the transducer until the desired imaging plane isacquired. The sonographer would then release the transducer and theapparatus should maintain the transducer position and apply thenecessary transducer pressure. Use of the system would provide asolution related to prolonged arm abduction, prolonged twisting andapplication of transducer pressure by the sonographer.

Notably, the system can be scaled up for industrial applications (e.g.,supporting heavy items) or down for entertainment applications (e.g.,toy) as required. The foregoing are examples only and are not intendedto limit the potential applications of the apparatus.

The embodiments of the present invention may also advantageously providea simpler and more effective solution to counterbalance loads of knownor unknown weight over the prior art. More specifically, the threeresilient member counterbalance system may preferably be adapted for amechanical arm, in which tools on the end of the arm can be translatedand rotated by a human user and will remain in position once the userreleases the arm. Furthermore, since the arm counterbalances the weightof the tool, the force the human user must exert to adjust the toolposition is substantially reduced.

The figures present one potential implementation of the concept. Thoseskilled in the art would understand that the system of the presentinvention does not necessarily need to be a parallelogram structure andalternative architectures such as a simple lever can be used.

A novel counterbalance system that contains two counterbalanceassemblies is provided. Each counterbalance contains two resilientmembers. One resilient member, the top resilient member, is common toboth assemblies resulting in a total of three resilient members. The armcounterbalance assembly counterbalances the payload of the arm. Apreload mechanism is used to preload the adjustable payload (K1) memberof the arm counterbalance assembly. The second counterbalance assemblyis used to counterbalance the force experienced by the user as theyrotate the preload mechanism to preload the resilient member.

The foregoing description has been presented for the purpose ofillustration and is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Other modifications, variationsand alterations are possible in light of the above teaching and will beapparent to those skilled in the art, and may be used in the design andmanufacture of other embodiments according to the present inventionwithout departing form the spirit and scope of the invention. It isintended the scope of the invention be limited not by this descriptionbut only by the claims forming a part hereof

1. A counterbalance system for engaging a payload having a load vectorin the direction of gravity, the system comprising: a payload (K1)member in communication with the payload to be engaged; a payloadcompensation (K2) member and an actuator compensation (K3) member incommunication with either end of the payload (K1) member; an actuator,having a loaded and an unloaded position, in communication with thepayload (K1) and the actuator compensation (K3) members, the payload(K1) and the actuator compensation (K3) members adapted to transfer anactuator energy during movement, of the actuator between the loaded andunloaded positions; a payload arm adapted to support the payload, havinga load-bearing and a neutral position, in communication with the payload(K1) and the payload compensation (K2) members, the payload (K1) and thepayload compensation (K2) members adapted to transfer a support energyduring movement of the payload arm between the load-bearing and neutralpositions; and whereby, movement of the actuator to the loaded positionwhen the payload arm is in the neutral position, transfers the actuatorenergy and the support energy to generate a lift vector at the payloadto counterbalance the load vector.
 2. The counterbalance system,according to claim 1, wherein the payload arm rotates about a firstpivot and the actuator arm rotates about a second pivot.
 3. Thecounterbalance system, according to claim 1, wherein the payload (K1)member, the payload compensation (K2) member and the actuatorcompensation (K3) member are adapted to exert an expansion force.
 4. Thecounterbalance system, according to claim 1, wherein the payload (K1)member, the payload compensation (K2) member and the actuatorcompensation (K3) member are compression springs.
 5. The counterbalancesystem, according to claim 2, further comprising first and second camsadapted to transfer the support energy between the payload (K1) memberand the payload compensation (K2) member and third and fourth cams totransfer the actuator energy between the payload (K1) member and theactuator compensation (K3) member.
 6. The counterbalance system,according to claim 5, wherein the first and second cams are mountedeccentrically in relation to the first pivot and the third and fourthcams are mounted eccentrically in relation to the second pivot.
 7. Thecounterbalance system, according to claim 1, wherein the payload (K1)member, the payload compensation (K2) member and the actuatorcompensation (K3) member are adapted to exert a compression force. 8.The counterbalance system, according to claim 7, wherein the payload(K1) member, the payload compensation (K2) member and the actuatorcompensation (K3) member are extension springs.
 9. The counterbalancesystem, according to claim 7, wherein the payload (K1) member and thepayload compensation (K2) member are attached eccentrically in relationto one another to facilitate transfer of the support energy and thepayload (K1) member and the actuator compensation (K3) member areattached eccentrically in relation to one another to facilitate transferof the actuator energy.
 10. The counterbalance system, according toclaim 1, further comprising a brake adapted to maintain the actuator ata position.
 11. The counterbalance system, according to claim 10,wherein the position corresponds with the load vector.
 12. A method ofengaging a payload having a load vector in the direction of gravityusing a counterbalance system, the method comprising: positioning apayload (K1) member in communication with the payload to be engaged;positioning a payload compensation (K2) and an actuator compensation(K3) member in communication with either end of the payload (K1) member;configuring an actuator, moveable between a loaded and an unloadedposition, for communication with the payload (K1) and the actuatorcompensation (K3) members to transfer an actuator energy during movementof the actuator between the loaded and unloaded positions; configuring apayload arm adapted to support the payload, moveable between aload-bearing and a neutral position, for communication with the payload(K1) and the actuator compensation (K2) members to transfer a supportenergy during movement of the payload arm between the load-bearing andneutral positions; and whereby, moving the actuator to the loadedposition when the payload arm is in the neutral position, transfers theactuator energy and the support energy to generate a lift vector at thepayload to counterbalance the load vector.
 13. The method of claim 12,whereby the payload arm rotates about a first pivot and the actuator armrotates about a second pivot.
 14. The method of claim 12, whereby thepayload (K1) member, the payload compensation (K2) member and theactuator compensation (K3) member are adapted to exert an expansionforce.
 15. (canceled)
 16. The method of claim 2, further comprisingfirst and second cams adapted to transfer the support energy between thepayload (K1) member and the payload compensation (K2) member and thirdand fourth cams to transfer the actuator energy between the payload (K1)member and the actuator compensation (K3) member.
 17. The method ofclaim 16, whereby the first and second cams are mounted eccentrically inrelation to the first pivot and the third and fourth cams are mountedeccentrically in relation to the second pivot.
 18. The method of claim12, whereby the payload (K1) member, the payload compensation (K2)member and the actuator compensation (K3) member are adapted to exert acompression force.
 19. (canceled)
 20. The method of claim 18, wherebythe payload (K1) member and the payload compensation (K2) member areattached eccentrically in relation to one another to facilitate transferof the support energy and the payload (K1) member and, the actuatorcompensation (K3) member are attached eccentrically in relation to oneanother to facilitate transfer of the actuator energy.
 21. The method ofclaim 12, further comprising the step of maintaining the actuator at aposition using a brake.
 22. The method of claim 21, whereby the positionof the brake corresponds to the load vector.